1. Field of the Invention
The present invention relates to a phosphor, a method of producing the phosphor, and a light-emitting apparatus including the phosphor; and more particularly to a nitride phosphor that is composed of a nitrogen-containing compound and can emit light in a green-to-yellow range, a light-emitting apparatus including the nitride phosphor, and a method for producing the nitride phosphor.
2. Description of the Related Art
Light-emitting apparatuses have been developed which include a light source and a wavelength conversion member that is excited by light from the light source and can emit different color light from that of the light source. As a result, the light-emitting apparatuses can emit light in various colors, based on the principle of additive light color mixing. For example, a light-emitting device emits the primary light in a short wavelength range corresponding to a range from ultraviolet to visible light so that a phosphor is excited by this emitted light. Accordingly, the primary light is at least partially converted into light having a different wavelength from the primary light. As a result, desired light (e.g., red, blue, green or the like) can be provided. Also, white light can be provided by additive color mixture of different light components.
Based on the principle, LED lamps have been used which include light-emitting diodes (hereinafter, referred to as LEDs) for many fields such as signal light, mobile phone, various types of illuminations, vehicle indicator, or various types of display apparatuses. In particular, with the increasing application of white LED light-emitting apparatuses including an LED and a phosphor to a liquid crystal display (LCD) backlight, an electronic flash, and the like, the use of the white LED light-emitting apparatuses is increased. In addition, recently, the white LED light-emitting apparatuses are tried to be used as a lighting apparatus. Since the white LED light-emitting apparatuses have advantages such as a long life and are mercury-free, in order to reduce the environmental load, it is expected that the white LED light-emitting apparatuses can serve as a replacement light source for fluorescent lamps.
A light-emitting apparatus including a white LED includes a blue LED and a yellow phosphor (for example, see Japanese Patent Publication No. JP 3,503,139 B). This light-emitting apparatus mixes blue light emitted from the LED with yellow light that is converted from the blue light from the LED by the yellow phosphor, whereby emitting white light. In this case, the phosphor used in this light-emitting apparatus is required to be efficiently excited by blue light with a wavelength from 420 to 470 that is emitted by the LED, and to emit light in a yellow range.
Also, the LED light-emitting apparatus is actively studied to increase its light emission properties. For example, in order to increase the brightness of white light, it is important to increase the intensities of both the light components for different colors. For this reason, a phosphor is required which can convert the primary light from the LED at high energy efficiency. In addition, in order to improve the color rendering property or color purity of white light, it is important that the light components have designed colors. To achieve this, the phosphor is required to have its peak wavelength in a predetermined wavelength range.
An yttrium aluminum garnet group phosphor activated by cerium is known as a yellow phosphor. Also, it is known that Y of this yellow phosphor can be partially substituted by Lu, Tb, Gd or the like, or Al of this yellow phosphor can be partially substituted by Ga or the like. The light wavelength of the yttrium aluminum garnet group phosphor activated by cerium can be widely adjusted by adjustment of composition.
In addition, as for phosphors other than these oxide phosphors, nitride phosphors are also known which have properties different from other inorganic compounds, although nitride phosphors are not easily produced as compared with the oxide phosphors. In particular Si3N4, AlN, BN, GaN, and the like are used in a variety of applications such as substrate materials, semiconductors, light emitting diodes, and are industrially produced. Also, nitride phosphors including three or more elements has been widely studied in recent years. Some nitride compounds were reported which were excited by a blue LED or near-ultraviolet LED, and emitted light in a range from blue to red.
Since the compounds or phosphors have different light emission spectrums, in the case where two or more of these compounds or phosphors are used, the white LED light-emitting apparatuses may have further improved properties. Accordingly, the white LED light-emitting apparatuses have been studied. For example, in the case where a (Sr, Ca)AlSiN3:Eu phosphor as nitride group phosphor is used in the white LED light-emitting apparatus disclosed in JP 3,503,139 B, the color rendering property and the color reproduction range can be improved (Japanese Patent Laid-Open Publication No. JP 2006-8,721 A).
Also, in the case the yttrium aluminum garnet group phosphor activated by cerium capable of emitting a yellow light component is replaced by some other phosphors, the color rendering property and the color reproduction range can be improved. La3Si6N11:Ce is disclosed as one of the some other phosphors.
See Japanese Patent Laid-Open Publication Nos. JP 2008-88,362 A and JP 2008-285,659 A.
The present invention is devised to solve the above problems. It is a main object of the present invention to provide a phosphor that includes a particular compound capable of improving its light emission properties as compared with La3Si6N11:Ce, a method for producing this phosphor, and a light-emitting apparatus including this phosphor.